Enhanced Performance of Asynchronous Multi-Cell VLC System Using OQAM/OFDM-NOMA

In this paper, an offset QAM/OFDM combined with non-orthogonal multiple access (OQAM/OFDM-NOMA) modulation technique is proposed and experimentally demonstrated in a multi-user and asynchronous multi-cell visible light communication (VLC) system. OQAM/OFDM-NOMA modulation can effectively improve system capacity and flexibility owing to non-requirement of cyclic prefix (CP) and flexible power allocation strategies. We evaluate the performance comparison between the proposed OQAM/OFDM-NOMA modulation and conventional OFDM-NOMA modulation in the multi-cell VLC system. Each cell consists of cell-center users with high signal-to-noise ratios (SNRs) and cell-edge users with low SNRs. According to the measured bit error rates (BERs) for the cell-center users and the cell-edge users, better user fairness can be achieved when the power ratio is 8 dB. Moreover, in the presence of asynchronous time offset for multi-cell VLC system, the experimental results show that the asynchronous time offset has a negligible impact on the cell-edge users using OQAM/OFDM-NOMA modulation. However, the asynchronous time offset will severely degrade the system performance in conventional OFDM-NOMA based VLC system. Therefore, for the user fairness and robustness against asynchronous time-offset, the proposed OQAM/OFDM-NOMA modulation can significantly outperform the conventional OFDM-NOMA modulation in the multi-user asynchronous multi-cell VLC system.